RESEARCH FINDINGS ON ABILITY GROUPING ARE INCONCLUSIVE BECAUSE NEITHER HETEROGENEITY NOR HOMOGENEITY HAS BEEN DEFINED WITH SUFFICIENT CLARITY. THE TENDENCY IN THESE STUDIES HAS BEEN TO STRESS THE PERFORMANCE OF THE PUPILS IN SUCH CLASSES RATHER THAN THE PERFORMANCE OF THE CLASS AS A WHOLE. IN A STUDY OF 181 CLASSES (4,705 PUPILS) HOMOGENEITY WAS MEASURED BY THE STANDARD DEVIATION OF CLASS PERFORMANCE ON THE FIRST TWO METROPOLITAN READING TESTS GIVEN IN TWO SUCCESSIVE YEARS. GROWTH WAS THEN DETERMINED BY THE DIFFERENCES IN CLASS MEANS ON THE TWO TESTS. THE SAME SUBJECTS WERE TESTED IN GRADE THREE AND FOUR, AND WERE DIVIDED INTO HIGH, AVERAGE, AND LOW LEVELS OF ACHIEVEMENT AND DEGREE OF HOMOGENEITY. (A STANDARD DEVIATION OF 6.0 THROUGH 8.9 MONTHS CHARACTERIZED "AVERAGE HOMOGENEITY.") FINDINGS SHOW AN INCONSISTENT GROWTH PATTERN--(1) ON THE WORD KNOWLEDGE SUBTEST, MEAN GROWTH WAS PRACTICALLY IDENTICAL FOR THE AVERAGE AND LOW HOMOGENEITY CLASSES, AND (2) ON THE READING SUBTEST, THE LOW HOMOGENEITY CLASSES SHOWED GREATER GROWTH THAN THE AVERAGE OR HIGH CLASSES. EVIDENCE OF INCONSISTENCY WAS ALSO EVIDENT WHEN VARIOUS COMBINATIONS OF INITIAL ACHIEVEMENT LEVEL AND CLASS HOMOGENEITY WERE ANALYZED. THEREFORE, NARROWING THE RANGE OF ABILITY IN CLASSES DOES NOT IPSO FACTO IMPROVE PUPIL ACHIEVEMENT. PROGRAMS DESIGNED SPECIFICALLY FOR THE SEVERAL ABILITY LEVELS ARE NEEDED AS A CONCOMITANT OF ABILITY GROUPING. THIS ARTICLE WAS PUBLISHED IN "THE URBAN REVIEW," VOLUME 2, FEBRUARY 1967. (NH)